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create¶
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Definition¶
-
create
¶ Explicitly creates a collection.
create
has the following form:create
has the following fields:Field Type Description create
string The name of the new collection. capped
boolean Optional. To create a capped collection, specify true
. If you specifytrue
, you must also set a maximum size in thesize
field.autoIndexId
boolean Optional. Specify
false
to disable the automatic creation of an index on the_id
field.Important
For replica sets, all collections must have
autoIndexId
set totrue
.size
integer Optional. Specify a maximum size in bytes for a capped collection. Once a capped collection reaches its maximum size, MongoDB removes the older documents to make space for the new documents. The size
field is required for capped collections and ignored for other collections.max
integer Optional. The maximum number of documents allowed in the capped collection. The size
limit takes precedence over this limit. If a capped collection reaches thesize
limit before it reaches the maximum number of documents, MongoDB removes old documents. If you prefer to use themax
limit, ensure that thesize
limit, which is required for a capped collection, is sufficient to contain the maximum number of documents.flags
integer Optional. Available for the MMAPv1 storage engine only to set the
usePowerOf2Sizes
and thenoPadding
flags. To set, specify one of the following values:0
corresponds tousePowerOf2Sizes
flag set tofalse
andnoPadding
flag set tofalse
.1
corresponds tousePowerOf2Sizes
flag set totrue
andnoPadding
flag set tofalse
.2
corresponds tousePowerOf2Sizes
flag set tofalse
andnoPadding
flag set totrue
.3
corresponds tousePowerOf2Sizes
flag set totrue
andnoPadding
flag set totrue
.
Note
MongoDB 3.0 ignores the
usePowerOf2Sizes
flag. SeecollMod
anddb.createCollection()
for more information.Defaults to
1
.New in version 2.6.
Changed in version 3.0.0: Add support for setting the new
noPadding
flag.Warning
Do not set
noPadding
if the workload includes removes or any updates that may cause documents to grow. For more information, see No Padding Allocation Strategy.storageEngine
document Optional. Available for the WiredTiger storage engine only.
New in version 3.0.
Allows users to specify configuration to the storage engine on a per-collection basis when creating a collection. The value of the
storageEngine
option should take the following form:Storage engine configuration specified when creating collections are validated and logged to the oplog during replication to support replica sets with members that use different storage engines.
The
db.createCollection()
method wraps thecreate
command.
Considerations¶
The create
command obtains a write lock on the
affected database and will block other operations until it has
completed. The write lock for this operation is typically short
lived. However, allocations for large capped collections may take
longer.
Examples¶
Create a Capped Collection¶
To create a capped collection limited to 64 kilobytes, issue the command in the following form:
Specify Storage Engine Options¶
New in version 3.0.
You can specify collection-specific storage engine configuration
options when you create a collection with
db.createCollection()
. Consider the following operation:
This operation creates a new collection named users
with a
specific configuration string that MongoDB will pass to the
wiredTiger
storage engine. See the WiredTiger documentation of
collection level options
for specific wiredTiger
options.